In recent years, accompanied by the diversification of various food materials, food additives, foods and beverages (including articles of taste), fragrances and cosmetics, sanitation materials, sundries, pharmaceuticals and the like, new demands for a flavor and fragrance to be used therein have been increasing, and concerns have been directed toward the development of aromatic materials having a highly-tasting unique odor. Particularly, with the recent uprush of the nature-oriented style of people and also from the safety point of view, great concerns have been directed toward the development of new aromatic materials derived from natural compounds, or identical or similar to the natural compounds, with regard to highly tasting fruity flavors and fragrances and tropical flavors and fragrances by which the natural environment can be imaged characteristically.
8-Mercaptomenthone has two chiral centers, and a total of 4 isomers including optical isomers are present. 8-Mercaptomenthone has been found as an essential-oil component of Buchu oil in the past studies, and is synthesized from d-pulegone and l-pulegone whose absolute structures of the natural product are already known. Additionally, according to the angle of rotation thereof, a (1S,4R) isomer has been found as the main component thereof, and a (1S,4S)-isomer as a diastereomer thereof has also been detected simultaneously. However, the mixing ratio thereof has not been disclosed (cf., Non-patent Reference 1).
In addition, synthesis method of each of these 4 isomers has been established and their sensory evaluation has been carried out. As a result, it has been reported that the (1S,4S)-isomer is particularly superior in odor, and the (1S,4R)-isomer also has a desirable odor. On the other hand, it has been reported as an evaluation result that the (1R,4R)-isomer and (1R,4S)-isomer accompany a rubber-like malodor. The products synthesized herein are the natural product having a mixing ratio of the (1S,4S)-isomer and (1S,4R)-isomer of 57:43, and the non-natural product having a mixing ratio of the (1R,4R)-isomer and (1R,4S)-isomer of 58:42 (cf., Non-patent Reference 2).
8-Mercaptomenthone has so far been used as a flavor and fragrance component (cf., Patent Reference 1). However, the 8-mercaptomenthone which has so far been used as the flavor and fragrance is a (1R)-isomer. This is because d-pulegone is used as the starting material which can be obtained easily and inexpensively from the nature. The pulegone used in Reference Example 1 of the Patent Reference 1 is also d-pulegone because its angle of rotation is +220, and the mixing ratio is 3:2. In addition, according to Reference Example 4, 8-mercaptomenthone (αD20=−12.0°) is obtained as a cis-trans mixture using isopulegone (αD20 124.2°) as the raw material. However, the mixing ratio is unknown.    Patent Reference 1: JP-B-49-24668    Non-patent Reference 1: J. Agric. Food Chem., 23(5), 943-50 (1975)    Non-patent Reference 2: Z. Lebensm Unters Forsch., 194, 372-376 (1992)